Please do a good documentation, with line by line explanation. I't takes long time but that is super cool for developer.
There is lots of tutorials but only few of them where you can read and do without additional googling

I think this is one of Magento's biggest weaknesses. If you look at other open source CMS' or Frameworks, they have better documentation (MODX being a good example). With Magento a lot of the official documentation is out of date and, sometimes more up to date info from third parties can be incorrect or hacking core files.

I note this has been planned now (for over a year ^^) and whilst there have been some improvements recently (such as the Alan Storm articles), I would love to know on the official status of this 'task' from Magento viewpoint!

Community can *add* value to documentation but nothing will ever start before core development team start publishing first - API, file format documentation, developer references, source layout, design docs ...

Every project out there who has a great user contributed documentation started with it written by core developers or with developers closely talking to people in charge of writing it. Not to mention release cycles with feature/bug/whatever freezes so documentation authors can finish/update whatever is needed *before* new release is published with clear procedure in place how to document backward incompatibilities.

This task involves a few things; some of which I'm sure the community would be more than happy to contribute, and some of which require some of developers of Magento to lead the way in.

First off, Magento needs an 'Intro To Magento'. Essentially, we need a document which says, "Start here if you're thinking about making eCommerce sites with Magento". This already exists in a few places, but it would be great if there a was a site with a big sign saying "Start Here Guys!'"

Next up, we need an "Architecture Overview". I'm not talking about low-level documentation; we need YOU to tell US what the architecture of Magento is. This document would allow developers to get a 'feel' for how Magento is organised and how things work, before looking at any code.

Then, there's a general 'howto do thingy X' set of guides; these guides could be written by both Varien developers and us standard users, and let people looking for knowledge on how to do one exact thing get at the information without needing to understand the entire codebase.

Finally, the actual code itself needs to be thoroughly documented. This is where some of us more advanced developers can help you. In fact, whenever I'm developing a new extension or rootling through the code, I often finding myself updating documentation and leaving myself notes. This is one area that could be drastically improved by everyone, and lead to a more mature and stable codebase.

I bought the 25$ magento user guide believing it would fill out some of the blanks but it was a total waste. I've been using magento for over a year and it didn't say anywhere that this was a beginner-from-scratch-never-seen-magento-before-product.

From day 1 of learning Magento, it takes about 3-4 months and then the official documentation is gone. From there, all you have is old forum posts, out-of-date wiki posts and occasionally brilliant but rare to be found bloggers.

I certainly would. The comments that benz001 have made highlight the documentation difficult. If you could define a standard, format and method then I am sure there would be a lot of people willing to support documenting. The notice board approach we have at the moment means that information can become quickly incorrect or worse never read.